Tracked vehicles and power drive apparatus for motivating tracked vehicles

ABSTRACT

An articulated tracked vehicle for agricultural harvesting which reduces damage to fields and can be driven on paved roads at reasonable speeds. The vehicle has front and rear elements, linked by an articulating joint which permits turning and rotation of one element with respect to the other. Each element is motivated by a pair of tracked power units which are hydraulically driven by a heavy duty differential between the units. Each power unit is rotatably mounted solely on a shaft sleeve of the differential and is free to oscillate vertically and independently to absorb irregularities in its path. Each unit includes an endless elastomeric track which has two rows of lugs on its inner surface. A novel drive mechanism engages these lugs to motivate the vehicle. A sealed transmission housing in each power unit protects key drive elements from environmental damage without interfering with operation of the unit. The transmission is centrally disposed within each power unit to provide further protection from damage.

FIELD OF THE INVENTION

The invention relates to tracked vehicles, and more particularly topower drive apparatus for tracked vehicles, which may have front andrear driven sections with an articulated connection for coupling andsteering the vehicles, and which may be hydraulically powered. Thepresent invention is especially useful in providing power units forsupporting or motivating agricultural harvesting apparatus such as headsand threshers which pick the crop. Power units have sometimes beencalled tractors.

BACKGROUND OF THE INVENTION

Off-road vehicles are commonly equipped with endless tracks rather thantires. Tracks have been found to be more useful than tires in rough ormarshy terrain, in that they are less prone to stress-induced failuresand to becoming bogged down. Tracks are desirable because they spreadtheir load (several thousand pounds for large agricultural power drives)over a larger surface area than do tires for similar loads, so that thetracked vehicles do not sink into the ground. For this reason, trackedpower drive vehicles have become widespread in off-road applicationssuch as construction, the military, recreational vehicles, snowgrooming, and some tracked vehicles have been used in agriculturalharvesting. See, for example, U.S. Pat. No. 5,176,573 issued to Paul Dowon Jan. 5, 1993.

Tracked vehicles commonly employ endless linked steel belts as tracks.These steel tracks are usually cleated on the outside to improvetraction. Steering is commonly accomplished by immobilizing one of thetracks and driving the other, causing the vehicle to pivot on itsstationary track. This maneuver requires high horsepower and also doessignificant damage to the surface beneath the vehicle. Therefore,steel-tracked vehicles are generally prohibited on paved roadways andmust be transported over the road on flatbed trucks.

Agricultural harvesters are used in plowed fields and even during wetweather; then, tracks are superior to tires for traction. An addedadvantage of tracks is that they do less damage to the soil by way ofcompaction and rutting. Recently, tracks made of elastomeric materialssuch as rubber or plastic have become available as alternatives to steeltracks. In agricultural harvesting, for example, rubber tracked vehiclescan be driven in the fields without significant damage to the soil andthen be driven over paved roads from field to field. It is a feature ofthe invention to provide improved tracked vehicles which can travel overthe road, and at reasonable speeds.

Tracked vehicles are known to be powered hydraulically, as disclosed in,for example, U.S. Pat. No. 3,447,619. A common drive utilizes alow-speed high-torque (LSHT) hydraulic motor. Such drives are powerfulbut are incapable of road speeds above about 15 miles per hour, whereasmany portions of the harvesting industry depend upon a road speed of 20miles per hour or higher to meet the demands of the harvesting schedule.Other drives use high-speed hydraulic motors with gear reduction, butthese are bulky, costly, and subject to high maintenance.

A common means of driving a rubber track is by forming a drive wheelwithin the power unit as essentially a sprocket and engaging the teethof the sprocket with holes formed in the track. This design has thedrawback that the sprocket teeth protrude through the rubber track andcan dig up the field and, more seriously, do damage to paved roadway.

Off-road tracked vehicles must handle rough, rocky terrain withoutconventional ride-softening suspension elements such as springs andshock-absorbers, which would interfere with precise location of thepicking and threshing mechanisms with respect to the crop and withrespect to each other. Track designs which have heretofore been proposedinclude designs which ride very roughly over objects in their path. Thetrack assembly must ride up on the object, reach its balance point, andthen fall forward, with no means within the action of the track toabsorb the shock of encountering the obstacle.

A drawback of conventional two-track vehicles resides in the long lengthof track required to support the vehicle. This exacerbates theaforementioned steering difficulty and surface damage. While four-trackvehicles having a two-part articulated chassis have been proposed, forexample, in U.S. Pat. Nos. 3,435,908; 3,741,331; 3,789,942; 3,937,289;and 4,072,203, they have not been suitable for heavy loads as requiredfor agricultural harvesting applications. It is a feature of theinvention to provide improved power drives which enable four-trackvehicles to haul heavy loads over rough terrain and with positionalstability needed to locate harvesting heads and threshing componentswith respect to the ground and to each other.

An additional drawback of conventional four-track vehicles is the needto limit the freedom of articulation of the joint between front and rearelements to left and right horizontally. This limits the ability of thevehicle to adapt to irregular terrain. This is because vertical rigiditymust be maintained between the two elements, particularly in designs inwhich independent vertical oscillation of each of the four power unitsis permitted. Without vertical rigidity, the articulating joint isvertically unstable in such conventional two-track vehicles. For thisreason, a simple ball-joint connection cannot be used. It is a featureof the invention to provide a joint for an articulated tracked vehiclewhich permits both horizontal (left and right) and rotational (about alongitudinal axis through the rear element) relative motion of the frontand rear elements, while maintaining vertical rigidity between theelements.

Track drive units commonly are designed with rugged drive elements suchas sprockets and chains which are exposed for easy repair andmaintenance, which has the drawback of making these elements vulnerableto damage. It is a feature of this invention to provide a power unit fora tracked vehicle wherein the drive elements are encased and located,within the unit for maximum protection of the elements, but in a waywhich does not interfere with operation and which still permits readyaccess for repairs and maintenance.

SUMMARY OF THE INVENTION

The invention provides an improved hydraulically powered tracked powerunit adapted for use on a tracked vehicle, and preferably on anarticulated tracked vehicle. An articulated tracked vehicle inaccordance with the invention may have two pairs of such power units.

More particularly, a power unit, which is provided in accordance with anembodiment of the invention, is driven by a chain-drive transmission,housed in a rugged, rigid sealed housing, which is also the primarystructural element of the power unit. The housing is rotatably mountedon a fixed sleeve of a differential on the vehicle, allowing the powerunit to pivot vertically about a horizontal axis in response toencountering an object in its path. This response, which is analogous tothe spring and shock absorber action in a wheeled vehicle, minimizes thevertical displacement of the axis. The transmission drives a memberwhich comprises both a road wheel and track drive sprocket, whichsprocket engages lugs formed on the inner surface of an endless trackand motivates the track thereby transmitting motive power to the groundbeneath the power unit.

Preferably, the chain drive transmission and its housing are locatedalong the longitudinal centerline of the power unit to remove them asfar as possible from hazards to either the left or right of the track.

The power unit may further comprise idler road wheels also within thetrack; a pair of oscillating idler bogies to aid in absorbingprotrusions above the surface of the road; and a device to maintainproper tension in the endless track.

An articulated tracked vehicle of the invention has a front and a rearchassis, connected by an articulating joint and adapted to be steered bymeans of functionally-opposed hydraulic cylinders to the left and rightof the articulating joint, whereby the front chassis can be turnedeither left or right with respect to the rear chassis. Additionally, ina preferred embodiment, the articulating joint comprises three sphericalbearings and a rotating link, the arrangement of which also permitslongitudinal relative rotation of the front chassis with respect to therear chassis while maintaining vertical rigidity of the joint.

Each chassis further comprises a rigidly-mounted hydraulically-powereddifferential unit having a rugged, sealed housing comparable in strengthto that of the power unit transmission housing. Two power units are eachrotatably disposed on the shaft sleeves of the two output power shaftsof the differential which extend in opposite directions from thedifferential. The two power units are thereby free to oscillatevertically with respect to the chassis and to each other. Thearticulated vehicle, comprising two chassis and four independent powerunits, can operate over very rough terrain with extreme stability andminimum vertical selective displacement.

The vehicle may be powered by an engine mounted on one of the chassis.An equipment module which may include harvesting or threshing devicescan be carried by the other chassis. The engine drives a masterhydraulic pump system, which in turn powers two independent hydraulicdrive elements, disc brakes for the front and rear differential units,and the hydraulic steering cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of an articulated tracked vehicle accordingto the invention, where the equipment and motors are shownschematically.

FIG. 2 is a top view of the vehicle of FIG. 1 with the superstructureremoved.

FIG. 3 is a top view like FIG. 2 with the vehicle of FIG. 2 in a turningmode.

FIG. 4 is an enlarged side elevation of one of the typical tracked powerunits of the vehicle of FIG. 1.

FIG. 5 is a sectional view taken along line 5--5 in FIG. 3 and FIG. 6,approximately middleway of the width of the track.

FIG. 6 is a fragmentary perspective view, partially in section, of thepower unit shown in FIGS. 4 and 5.

FIG. 7 is a sectional view taken along line 7--7 in FIG. 4.

FIG. 8 is a view like FIG. 7, enlarged to show the rear of the unit,including the driven sprocket and drive wheels, in greater detail thanin FIG. 7.

FIG. 9 is a view like FIG. 7, enlarged to show in greater detail themiddle portion of the unit of FIG. 7, including the drive sprocket andmount on which the unit can rotate.

FIG. 10 is a view like FIG. 7, enlarged to show the front of the unit,including the arrangement of idler wheels, in greater detail than inFIG. 7.

FIG. 11 is a sectional view taken along line 11--11 in FIG. 7.

FIG. 12 is an enlarged side elevation of the central area of FIG. 1,showing details of the articulating joint.

FIG. 13 is an enlarged view of the central area of FIG. 2, showingdetails of the articulating joint.

FIG. 14 is an isometric view of the articulating joint of FIGS. 12 and13, showing the joint in articulation and the limitation of rotation ofone chassis with respect to the other imposed by the rotation limitingplate.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the figures, wherein like numbers are given to likeelements in the different drawings, in FIG. 1 is shown an articulatedtracked vehicle 10 in accordance with the invention. The vehicle has afront driven element 12 and a rear driven element 14 which aresubstantially identical mechanically. Front element 12 carries asuperstructure 16 comprising an engine module 18 which includes a masterhydraulic pump, both shown schematically, and which powers both elements12 and 14 of vehicle 10. Superstructure 16 also includes an operatorcompartment 20 for control of the driving functions of the vehicle andthe equipment functions of the equipment module 22 carried by rearelement 14. Alternatively, superstructure 16 can be sized or positionedon front element 12 such that some elements of equipment module 22 canbe borne by front element 12. Front element 12 and rear element 14 canbe the same or different in length, width, and height.

In a preferred embodiment, front and rear elements 12 and 14 are coupledby an articulating joint 230, as shown variously in FIGS. 1, 2, 3, 12,13 and 14. Shown are three substantially identical spherical bearingunits: upper 232, lower rear 252, and lower forward 272. These threebearing units are coplanar in a vertical plane containing thelongitudinal axis of vehicle 10 when vehicle 10 is on level ground.Commercially-available bearing units, such as Torrington 22 SF-36Spherical Bearings, available from The Torrington Co., Torrington,Conn., are suitable for this purpose.

Bearing unit 232 is mounted in the flanges of upper bearing mount 234 onrear chassis 34'. Bearing unit 252 is mounted in the flanges of rearchassis lower bearing mount 254 directly below and co-linear withbearing unit 232. The race of bearing unit 232 is connected to frontchassis 34 by bearing mount 236. Bearing 272 is mounted on front chassis34 in the flanges of lower forward bearing mount 274, directly forwardof bearing unit 252. The races of bearing unit 252 and 272 are connectedby rotatable link 262, said link thereby being allowed to rotate aboutits longitudinal axis in response to rotation of front element 12relative to rear element 14.

In operation, bearings 232 and 252 constitute a vertical hinge, allowingfront element 12 to turn left or right relative to rear element 14 asshown in FIG. 3. Additionally, the three spherical bearings 232, 252,272, and rotatable link 262 cooperate to allow longitudinal rotation offront element 12 relative to rear element 14 while maintaining verticalrigidity of articulating joint 230. The longitudinal axis of the vehiclecan bend only left or right, never up or down. Rotation of link 262 islimited by rotation limiting plate 264 to 15° from horizontal, eitherclockwise or counterclockwise.

FIG. 14 shows the relationship of rotatable link 262 to rotationlimiting plate 264. This limitation is necessary to prevent damage tobearings 232, 252 and 272.

Alternatively, front and rear elements 12 and 14 can be coupled bymounting a vertical hinge (not shown) in place of bearings 232 and 252,and by eliminating bearing 272 and fixedly connecting link 262 to frontchassis 34. This hinge arrangement provides full freedom of motionlaterally for steering and is rigid vertically, but does not permitrotation of one chassis element with respect to the other.

Also shown in FIG. 1 are right side front and rear tracked power units30 and 32, respectively, the construction and operation of which isdescribed herebelow.

FIG. 2 is a top view of the vehicle in FIG. 1 with the superstructureremoved for clarity of presentation, showing the close similarity indesign between the front and rear driven elements 12 and 14. FIG. 2shows the general layout of the vehicle comprising front right and lefttracked power units 30 and 31 on front element 12, and rear right andleft power units 32 and 33 on rear element 14.

Front element 12 includes a structural chassis 34. Front differential 36is a conventional, heavy duty differential having a power input shaft 38and two diametrically opposed power output shafts 39 and 39' (notvisible in FIG. 2). The housing 40 of differential 36 is strong enoughto withstand the torsional loads exerted on it by the attachment andaction of the power units as is described herebelow.

Power output shafts 39 and 39' are carried in fixed sleeves 41 and 41',respectively, which are integral with differential housing 40 and arerigidly attached to the underside of chassis 34 by clamps 42 and 42',respectively.

Power input shaft 38 is connected to a variable displacement hydraulicmotor 44 which is rigidly mounted on chassis 34 and is supplied withhigh-pressure hydraulic fluid from the master hydraulic pump (means notshown). Fixed on power input shaft 38 is disc 46 which cooperates withchassis-mounted caliper 48 as a disc braking system for front element12. Caliper 48 is also hydraulically supplied by the master hydraulicpump. Braking is accomplished by de-powering of the differentialhydraulic drive motor and/or pressurizing of the hydraulic brakecaliper.

The design and operation of rear driven element 14 is virtuallyidentical with that of front element 12. The analogous parts are rearstructural chassis 34'; rear differential 36'; rear differential powerinput shaft 38'; rear differential housing 40'; rear differential fixedsleeves 43 and 43'; rear variable displacement hydraulic motor 44'; rearbrake disc 46'; and rear brake caliper 48'.

FIGS. 2 and 13 also show the layout of the steering mechanism. Right andleft double-action hydraulic steering cylinders 50 and 51 are connectedat their forward ends to front chassis 34 on opposite sides ofarticulating joint 230 by ball joints 52 and 53, respectively, and attheir rear ends to yoke 54 by ball joints 55 and 56, respectively. Yoke54 is a rigid member on rear chassis 34'.

The vehicle is turned, or steered, as is shown in FIG. 3. Right steeringcylinder 50 is extended while left steering cylinder 51 issimultaneously retracted, causing front element 12 to turn to the leftwith respect to rear element 14. Rear element 14 will follow frontelement 12 on nearly the same track. The front and rear differentialspermit the right side power units 30 and 32 to turn faster than the leftside power units 31 and 33, thereby turning the vehicle in an arc to theleft with minimal added horsepower required and with minimal scrubbingand damage to the surface under the tracks. Turning to the right isaccomplished by reversing the actions of steering cylinders 50 and 51.Ball joints 52, 53, 55 and 56 are designed and placed such that even atmaximum stroke of the cylinders there is no interference between thetracks of the power units on the front and rear chassis.

FIG. 4 is an enlarged side elevation of right side tracked power unit 30of vehicle 10. A sealed structural housing 78 is shown which protectsdrive elements within it as well as being the principal structuralmember of power unit 30. Rotating axle 76, connected to the drive withinhousing 78, protrudes through both sides of housing 78. A telescopingstructural member 75 (not visible in FIG. 4) is disposed in a fixedmember 75' on the forward end of housing 78 to carry an idler fixed axle86 (not visible in FIG. 4.) A bogie fixed axle 88 is disposed on theunderside of structural housing 78. Outer track drive sprocket 68 isaffixed by nuts and bolts 72 to a stepped hub 74 mounted on rotatingaxle 76. Endless track 60 is shown with outboard drive lugs 62 affixedto its inner surface and engaging with outer drive bars 64 affixed tothe tips of spaced teeth 66 of track drive sprocket 68 near the rear endof power unit 30. Lugs 62 have rounded valleys 70 between them, suchthat the valleys fit snugly around bars 64 and the lugs fit snuglybetween spaced teeth 66 when the track is travelling around drivesprocket 68. Bars 64 are also further affixed laterally to a smoothouter drive wheel 77 which is sized to fit snugly against the innersurface of endless track 60 inboard of lugs 62.

FIG. 4 also shows outer idler wheel 80 near the front end of power unit30. Outer idler wheel 80 is affixed by bolts 82 to outer hub 84 whichrotates on idler fixed axle 86 (not visible in FIG. 4). Outer idlerwheel 80 is bevelled around its circumference and is sized to fit snuglyagainst the inner surface of endless track 60 inboard of outboard drivelugs 62. The arrangement of idler wheels is shown in more detail inFIGS. 7 and 10.

An outer bogie, comprising a swing arm 90 carrying two outer bogiewheels 92, is mounted on bogie fixed axle 88. Outer bogie wheels 92 arealigned longitudinally with outer drive wheel 77 and with outer idlerwheel 80. Swing arm 90 is free to oscillate about fixed axle 88 inresponse to protrusions in the road under the track, thereby providingfirm yet resilient support for track 60. This greatly reduces theundesirable characteristic of formerly-proposed track designs whichforce the entire vehicle to ride unforgivingly up and over suchprotrusions. The arrangement of the bogie is shown in greater detail inFIGS. 6, 7 and 9.

FIG. 4 also shows an access panel 94 on the outside of housing 78whereby drive components within housing 78 are easily reached forassembly, repair, or maintenance.

FIG. 4 also shows part of the mechanism for maintaining tension inendless track 60, including hydraulic tensioning cylinder 106. Thismechanism is shown more clearly in FIGS. 5 and 6.

FIG. 5 shows elements of a chain-drive transmission, tensioningmechanism, and conveyance. Since FIG. 5 is a sectional view throughpower unit 30, it shows elements inboard of housing 78 not visible inprevious figures.

Differential output shaft 39 extends through the inner sidewall ofhousing 78 and is fitted on its end with transmission drive sprocket 96.Rotating axle 76 is carried in bearings 126 mounted with seals in thesidewall of housing 78, as is shown in detail in FIG. 8. Driventransmission sprocket 100 is fixed on axle 76. Roller drive chain 102 isdisposed about drive sprocket 96 and driven sprocket 100. Sealed housing78 also serves as an oil bath, allowing the chain and sprockets to bebathed in oil continuously during operation.

Power unit 30 is substantially symmetrical about a longitudinal axisthrough housing 78. Thus the outer conveyance elements described in FIG.4 have mirror image inner counterparts. Shown in FIG. 5 are an innerdrive wheel 108, an inner track drive sprocket 110 carrying inner drivebars 112 affixed to sprocket teeth 114 and to inner drive wheel 108. Aninner bogie assembly comprising inner bogie swing arm 116, inner bogiewheels 118, and inner bogie wheel axles 120 is shown disposed on theinner end of bogie fixed axle 88. An inner idler wheel 122 and its hub124 are shown disposed on the inner portion of axle 86.

As noted previously, idler fixed axle 86 is mounted at the forward endof telescoping structural member 75, and is retained there by clamp 104.Telescoping member 75 moves within a fixed outer member 75' rigidlyattached to housing 78. Hydraulic tensioning cylinder 106 is connectedby shackles to housing 78 at its rear end and to telescoping member 75at its forward end. Cylinder 106 is controllably supplied with highpressure hydraulic fluid (not shown), whereby axle 86 is urged away fromaxle 76 to maintain proper tension in endless track 60.

FIG. 6 is a fragmentary perspective view, partially in section, of aportion of power unit 30, showing the longitudinal symmetry of the powerunit about housing 78 and its relationship to differential 36 and fixedsleeve 41.

FIG. 6 also shows the design of the inner surface of endless track 60and how it relates to a portion of the drive and conveyance elementsdescribed in FIGS. 4 and 5. Outer drive lugs 62 are formed in a rowalong the outer edge of the inner surface of track 60. The purpose oflugs 62 is to mesh with drive bars 64 and teeth 66 on track drivesprocket 68. A mirror image inner row of lugs 164 (not shown in FIG. 6)is formed on track 60 to mesh with the counterpart inner drive elementspreviously described. The load bearing conveyance elements comprisingouter and inner drive wheels 77 and 108, outer and inner bogie wheels 92and 118 (not shown), and outer and inner idler wheels 80 and 122(neither shown) run against the inner surface of track 60 between thetwo rows of lugs, thereby distributing the vertical load onto the trackand providing lateral stability for the track lugs against the sides ofthese elements.

FIG. 7 is a horizontal sectional view of power unit 30 showing therelationship of inner and outer drive and conveyance elements to thestructural housing and to the inner surface of the track. It also showsthe relationship of the differential and its fixed sleeve to thestructural housing. For clarity of presentation, the power unit elementsin FIG. 7 are described in greater detail in FIGS. 8, 9, and 10.

FIG. 8 shows details of the bearings and seals which permit axle 76 torotate through sealed housing 78. The assembly is designed to have theinner bearings and seals installed prior to installation of the axle andtransmission drive sprocket.

Inner bearing 126 is pressed into inner bearing retainer 128 which alsocomprises inner shaft face seal 130. The openings in the inner and outerwalls of housing 78 are sized for insertion of inner bearing retainer128 from the outside of power unit 30. Retainer 128 is secured to innerretainer ring 136 by bolts 138, and ring 136 is secured to housing 78 bybolts 140. Rotating axle 76 comprising inner and outer bearing lands 142and 144 and having been previously fitted with driven sprocket 100 isinserted through inner bearing 126. Outer bearing retainer ring 146 issecured to the outer wall of housing 78 by bolts 148. Outer bearingretainer 150 comprising outer bearing 152 and outer shaft face seal 154is secured to retainer ring 146 by bolts 156. The hub 111 for innertrack drive sprocket 110 is mounted onto the inner end of axle 76, andthe assembly of drive sprocket 110 and drive wheel 108 is secured to hub111 by bolts 158. Similarly, the hub 74 for outer track drive sprocket68 is mounted on the outer end of axle 76, and the assembly of sprocket68 and drive wheel 77 is secured to hub 74 by bolts 160.

FIG. 8 also shows outwardly flared flanges 162 at the outer rim of outerdrive wheel 77 and the inner rim of inner drive wheel 108. These flangesalternate with drive bars 64 and 112, and provide lateral stability ofthe drive wheels between outer drive lugs 62 and inner drive lugs 164.

FIG. 9 shows the arrangement of elements by which power unit 30 isattached to differential 36 (not shown). Shaft sleeve 41 comprisessealing land 166, inner bearing land 168, and outer bearing land 170.Sleeve 41 is threaded at its outer end to accept retainer nut 172 andlocking nut 172'. Hub 174 containing inner bearing 176, outer bearing178, and sleeve seal 180 is fitted to sleeve 41 and secured by nuts 172and 172'. After power unit 30 is properly aligned with differential 36,hub 174 is secured to thrust plate 181 on housing 78. This is the onlystructural connection of power unit 30 to vehicle 10. Its design andlocation at substantially the longitudinal center of power unit 30permits unit 30 to oscillate freely about sleeve 41 in response tovariations in terrain.

Differential power output shaft 39 is adapted to receive shaft bearing182 in shaft bearing retainer 184, which is secured to hub 174 by bolts186. These bolts are accessible through access opening 188 in housing78. Transmission drive sprocket 96 also is fitted and secured to the endof drive shaft 39 through opening 188.

FIG. 10 shows the arrangement of bearings and seals whereby outer andinner idler wheels 80 and 122 are mounted on idler axle 86. Whenassembly is complete, all bearing surfaces are sealed from externalcontamination. Axle 86 is secured to telescoping structural member 75 byclamp 190 and bolts 192, as is also shown isometrically in FIG. 6. Innerand outer environmental seals 194 and 196 are fitted to axle 86 onopposite sides of member 75 and secured by bolts 198. Inner idler wheelhub 124 adapted as a bearing retainer for first and second inner idlerwheel bearings 202 and 204 is fitted to axle 86 and secured by thrustwasher 206 and castellated axle nut 208 which is torque-loaded andpinned on the threaded inner end of axle 86. Inner idler wheel 122 issecured to hub 124 by bolts 210. Protective cap 212 is placed over nut208 and secured to hub 124 by bolts 214.

Similarly, outer idler hub 84 containing first and second outer idlerwheel bearings 216 and 218 is fitted to axle 86 and secured by thrustwasher 220 and castellated axle nut 222 which is torque-loaded andpinned on the threaded outer end of axle 86. Outer idler wheel 80 issecured to hub 84 by bolts 82. Protective cap 226 is placed over nut 222and secured to hub 84 by bolts 228.

FIG. 11 shows the mechanical relationship of differential 36, chassis34, and power unit 30. Sleeve 41 of differential right side power outputshaft 39 is rigidly secured to chassis 34 by means of clamp 42. Thedifferential is also similarly secured to the left side of the chassis(not shown) such that there can be no relative motion between thedifferential and the chassis. Power unit 30 is disposed on the ends ofsleeve 41 and shaft 39 as previously described regarding FIG. 9.

FIG. 11 also shows the disposition of inner and outer bogie wheels 118and 92 on bogie axle 88 symmetrically about housing 78 in power unit 30,and the vertical and lateral support afforded power unit 30 by theaction of both bogie assemblies between the two rows of lugs 62 and 164on endless track 60.

What is claimed is:
 1. A power unit for a tracked vehicle comprising:a)a housing capable of supporting said unit and disposed longitudinally insaid unit comprisingi) a first lateral bore near a first end of saidhousing, ii) a first fixed axle laterally disposed on said housing neara second end thereof, and extending beyond opposite sides of saidhousing, iii) a second lateral bore at a longitudinally central locationof said unit; iv) a second fixed axle laterally disposed on an undersideof said housing at a longitudinally central location of said unit, andextending laterally beyond the sides of said housing; b) a rotatableaxle disposed in said first lateral bore and extending beyond saidopposite sides of said housing; c) a chain drive transmission disposedwithin said housing comprisingi) a drive sprocket, the axis of rotationof which is disposed on the centerline of said second lateral bore, ii)a driven sprocket fixed on said rotatable axle, and iii) a drive chainoperationally connecting said drive sprocket and said driven sprocket;d) first and second toothed drive wheels coaxially disposed and fixed onsaid rotatable axle on opposite sides of said housing; e) first andsecond idler wheels disposed on said first fixed axle on opposite sidesof said housing; and f) an endless track disposed with an inner surfacethere in contact with said toothed drive wheels and said idler wheels,and having lugs formed on a portion of said inner surface, said lugsbeing spaced to mesh with said toothed drive wheels, whereby saidendless track is caused to rotate in response to power applied to saidpower shaft.
 2. A power unit of claim 1 wherein said chain drivetransmission is disposed on substantially the longitudinal centerline ofsaid power unit.
 3. A power unit of claim 1 further comprising first andsecond bogies disposed on said second fixed axle on opposite sides ofsaid housing.
 4. A power unit of claim 1 wherein said endless trackcomprises an elastomeric material.
 5. A power unit of claim 4 whereinsaid elastomeric material comprises rubber or plastic.
 6. A power unitof claim 1 further comprising means for establishing and maintainingtension in said endless track.
 7. A power unit of claim 1 wherein saidhousing provides a sealed container for an oil bath for said chain drivetransmission.
 8. A power unit of claim 1 wherein said lugs on said innersurface of said endless track are disposed in first and second rows, onerow along each edge of said inner surface, wherein said lugs are engagedby said first and second toothed drive wheels, respectively.
 9. A powerunit of claim 1 wherein each of said first and second toothed drivewheels comprises:a) a hub disposed on and fixed to said rotatable axle;b) a track drive sprocket having teeth and valleys and disposedcoaxially on said hub; c) a driven road wheel having outwardly flared,separated, inwardly-directed radial flanges on an inner surface thereof,said driven road wheel being in operational contact with the innersurface of said track and disposed inboard of said track lugs; and d)bars affixed on and transversely to each of said teeth and between eachof said radial flanges of said driven road wheel whereby said road wheelis affixed to said track drive sprocket, the spacing of said teeth andsaid lugs being chosen to cause said teeth and bars to mesh with saidlugs on said endless track.